The purpose of the work is to obtain the nucleotide sequence of the regulatory regions of the BK virus genome. A comparison with SV40 may help us better understand gene structure and function of the papovavirus. The nucleotide sequence of the initiation site of DNA replication and the early region of the genome which codes for small t-antigen has been obtained. The BKV genome in this region shows approximately 70% sequence homology with SV40.